Method of producing a sense of depth in a painting by imitating the effect of atmosphere that makes objects look paler, bluer, and hazier or less distinct in the middle and far distance. The term was coined by Leonardo da Vinci, but the technique can be seen in ancient Greco-Roman wall paintings (e.g., at Pompeii). It was discovered that dust and moisture in the atmosphere caused the scattering of light passing through it; short-wavelength light (blue) is scattered most and long-wavelength light (red) least. Italian painters in Leonardo's time used the device; it was exploited by 15th-century northern European artists and later by J.M.W. Turner.

In zoology, one of a pair of slender, segmented sensory organs on the head of insects, myriapods (e.g, centipedes, millipedes), and crustaceans. Antennae of insects, which are movable, are believed to serve as both tactual and smell receptors; in some species, the development of elaborate antennal plumes and brushlike terminations has led to the suggestion that they also serve for hearing. Evidence supports this idea only for the mosquito, whose antennae are attached to specialized structures stimulated by vibrations of the antennal shaft. In social insects (e.g., ants), antennae movements may serve as communication.